Given a number N, the task is to find the Nth Tridecagonal number.
A tridecagonal number is a figurate number that extends the concept of triangular and square numbers to the tridecagon(a thirteen-sided polygon). The Nth tridecagonal number counts the number of dots in a pattern of N nested tridecagons, all sharing a common corner, where the ith tridecagon in the pattern has sides made of ‘i’ dots spaced one unit apart from each other. The first few tridecagonal numbers are 1, 13, 36, 70, 115, 171 …
Examples:
Input: N = 2
Output: 13
Explanation:
The second tridecagonal number is 13.
Input: N = 6
Output: 171
Approach: The Nth tridecagonal number is given by the formula:
Below is the implementation of the above approach:
C++
#include <bits/stdc++.h>
using namespace std;
int Tridecagonal_num( int n)
{
return (11 * n * n - 9 * n) / 2;
}
int main()
{
int n = 3;
cout << Tridecagonal_num(n) << endl;
n = 10;
cout << Tridecagonal_num(n) << endl;
return 0;
}
|
Java
class GFG{
static int Tridecagonal_num( int n)
{
return ( 11 * n * n - 9 * n) / 2 ;
}
public static void main(String[] args)
{
int n = 3 ;
System.out.print(Tridecagonal_num(n) + "\n" );
n = 10 ;
System.out.print(Tridecagonal_num(n) + "\n" );
}
}
|
Python3
def Tridecagonal_num(n):
return ( 11 * n * n - 9 * n) / 2
n = 3
print ( int (Tridecagonal_num(n)))
n = 10
print ( int (Tridecagonal_num(n)))
|
C#
using System;
class GFG{
static int Tridecagonal_num( int n)
{
return (11 * n * n - 9 * n) / 2;
}
public static void Main(String[] args)
{
int n = 3;
Console.Write(Tridecagonal_num(n) + "\n" );
n = 10;
Console.Write(Tridecagonal_num(n) + "\n" );
}
}
|
Javascript
<script>
function Tridecagonal_num(n)
{
return (11 * n * n - 9 * n) / 2;
}
let n = 3;
document.write(Tridecagonal_num(n) + "</br>" );
n = 10;
document.write(Tridecagonal_num(n));
</script>
|
Time complexity: O(n) for given n, because constant operations are done
Auxiliary Space: O(1)
Reference: https://en.wikipedia.org/wiki/Polygonal_number
Last Updated :
19 Sep, 2022
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